Patent GB-759853-A (GB)
Title: Improvements in the low temperature separation of air
IPC: F25J3/04
Filed: 1953-04-07
Abstract: 759,853. Low temperature separation of air. AIR REDUCTION CO., Inc. April 7, 1953 [Dec. 19, 1952], No. 9406/53. Class 8(2). In an air separation process primarily for the production of pure liquid oxygen using high and low pressure rectifiers 37, 59 all the nitrogen effluent from column 37 is condensed e.g., in a passage 85 from oxygen reboiler 63 and in a condenser 89, and substantially all the condensed nitrogen is returned through a duct 47 to the column 37 as reflux whereby the production of high purity nitrogen is promoted a small portion of which e.g. three per cent may be delivered through a duct 97. In operation air from a compressor 13 having been freed of carbon dioxide in one or other of passages 21, 25 of a reversing heat exchanger 23 controlled by a switching valve 17 traverses a duct 31 and enters a scrubber portion 39 of the high pressure column 37 from which krypton and xenon are discharged through a duct 43, oxygen-rich liquid is transferred to the column 59 through a duct 55, an expansion valve 57, an argon liquefier 147, a condenser 144 of an argon separating column 140 and a duct 58, and nitrogen-rich liquid from a trough 53 traverses a duct 73 and valve 79 to provide reflux for the column 59. Liquid oxygen from the base of column 59 supplies the reboiler 63 and the resulting oxygen vapour is returned through a duct 65. Waste nitrogen from the head of column 59 is discharged through a duct 33, one or other of passages 21, 25 undergoing deriming and the valve 17 to atmosphere. Argon-rich gas is fed through a duct 142 to the column 140 from which liquid oxygen is returned through a duct 161 to the column 59, and crude argon gas traverses a duct 145 and the liquefier 147 and the liquid argon is discharged through a duct 153. The concentration of argon at the level of duct 142 is maintained at an optimum value of 6 per cent by controlling a bleed valve 173 by means of an argon gas analyser 177. Condensation of the high-pressure nitrogen in condenser 89 is effected by heat exchange with nitrogen circulating in a closed circuit comprising a compressor 117 discharging through a passage 121 of a heat exchanger 123 and from which passage the major portion of the nitrogen is bled through a duct 125 and expanded in an engine 127 and returned to the compressor intake along a passage 131 to effect cooling of the passage 121. The remaining nitrogen from passage 121 having been cooled by the expanded portion is itself expanded at a valve 134 and traverses a boiling tube 41, a further expansion valve 101, the tubes 91 of condenser 89 and a duct 105 leading to a non-reversing passage 27 in the heat exchanger 23, a duct 111 and the compressor inlet. Prior to entry of recycle nitrogen to the passage 27 a major portion is bled from duct 105 through a duct 107 to join the nitrogen leaving the engine 127 and entering the passage 131, and at a point between the ends of passage 27 a minor portion of the recycle nitrogen is bled through a duct 109 to the passage 131 whereby the temperature gradient of the exchanger 23 is controlled. Specifications 759,897, 759,898 and 759,899 are referred to.